1. Field of the Invention
This invention relates to a pipe stopper method and apparatus and more particularly to an expandable plug assembly movable into and out of a pipeline to block or permit flow of fluid therethrough by rotation of a nonrising stem to exert both external and internal forces upon an expandable plug to expand the plug outwardly into sealing engagement with the interior of the pipeline.
2. Description of the Prior Art
It is well known in the art of distribution pipelines, either gas or water, to insert a deformable pipe stopper into a transverse cut-out portion of the pipeline and deform the pipe stopper to shut off the flow of fluids through the pipeline. When a pipeline is severely ruptured, and in order to minimize the number of customers having interrupted service, it is preferred that the pipeline be sectionalized without the need to add a full cut-in type valve which is generally installed during initial construction of the pipeline. Sectionalizing with full cut-in type valves is a complex operation that is very time consuming.
An add-on stopper valve, as disclosed in U.S. Pat. No. 3,799,182, utilizes an add-on pipe stopper attached to an existing pipeline as an alternative to the full cut-in type valve. This type of add-on pipe stopper does not require shutdown or interruption of pipeline service during the installation of the stopper valve, as do the full cut-in type valves. This type of add-on stopper valve reduces the time and costs of installation of the pipeline sectionalizing operation. More valves can be installed to complete the sectionalizing program with a minimum of interruption to the pipeline customers. U.S. Pat. Nos. 2,763,282 and 2,740,606 also disclose stopper elements deformable in a pipeline to shut off fluid flow.
To install the add-on stopper valve as disclosed in U.S. Pat. No. 3,799,182 a fitting is welded to the pipeline at the location of cutting an opening into the pipeline at the point where flow through the pipeline is to be interrupted. After the fitting is installed a gate valve is secured to the fitting and a saw chamber assembly is threadedly secured within the gate valve assembly. The gate valve is opened and a saw blade is inserted through the valve and the fitting into contact with the pipeline to cut a hole or opening into the pipeline. Thereafter, the saw blade is retracted into the saw chamber assembly and the gate valve is closed to prevent the escape of fluid from the cut pipe. An insertion chamber assembly for the pipe plug is threadedly engaged to the gate valve and the pipe plug is pushed through the open gate valve and affixed to a holding chamber. Thereafter both the insertion chamber assembly and the gate valve are removed. A completion bonnet is then attached to the holding chamber. Manipulation of the completion bonnet extends the pipe plug into the pipeline. The pipe plug is solid and when compressed against the side wall of the pipe deforms and spreads to close off the pipe.
One of the problems encountered with stopper devices of the above type is distortion of the plug resulting from excessive force application to deform the plug. If the magnitude of the external compressive forces applied to a solid elastomeric plug exceeds a predetermined limit, then the deformed plug will separate from the wall of the pipeline forming a leak path around the plug. Thus precaution must be exercised to prevent this excessive force application. However, operators have a tendency to apply excessive force in an effort to assure a bubble-tight fit. Without a satisfactory means of limiting the force application beyond the point where distortion begins, the operator must rely on judgment and experience to limit the force application. It is also the practice to coat the plug prior to insertion with a suitable material, such as grease, to seal a leak path which develops upon use of the pipe plug.
As an alternative to the solid one piece elastomeric stoppers disclosed in U.S. Pat. Nos. 3,799,182 and 2,763,282, U.S. Pat. No. 2,740,606 utilizes a pipe stopper that is internally expandable and includes a cylindrical plug sleeve of a relatively thin wall thickness. The sleeve is preferably formed of resilient material and has radial vanes. Wedging members are positioned within the sleeve and upon rotation of a screw, the wedges are moved on the vanes to either expand or contract the sleeve. In addition, the sleeve is also expanded by the flow of fluid on the upstream side of the stopper into the sleeve. U.S. Pat. No. 3,040,779 also discloses a plug device that includes a thin walled packing element that is adapted to be inflated by a pressure medium. These devices must be maintained under pressure to retain a fluid tight seal in the pipeline. Also due to the thin wall structure they are not as durable as solid plugs.
While it has been suggested to provide add-on stopper valves that utilize deformable plugs that are deformed by external forces applied to the plug and expandable plugs that are expanded by internal forces applied to the plug, there is need for an expandable stopper that does not require the use of fluid forces to apply an internal expanding pressure on the plug and possesses the durability of deformable solid plugs. The expandable plug must be capable of repeated cycles of expansion and contraction into and out of sealing relation with the pipeline and provide continued stopper service. The expandable plug must also be sufficiently durable to insure that upon each expansion cycle it completely engages the interior of the pipeline. Also, the expansion of the plug must be limited so as not to apply excessive forces resulting in distortion and leak paths around the plug.